Supported Platforms
Related Documentation
- MX Series
- VPLS Multihomed Layer 2 Ring and MPLS Infrastructure Overview in the Junos OS Layer 2 Switching and Bridging Library for Routing Devices
- Multicast Snooping on MX Series Routers in the Junos OS Layer 2 Switching and Bridging Library for Routing Devices
- Configuring Multicast Snooping to Ignore Spanning Tree Topology Change Messages in the Junos OS Layer 2 Switching and Bridging Library for Routing Devices
- Example: Configuring Multicast Snooping for a Bridge Domain in the Junos OS Layer 2 Switching and Bridging Library for Routing Devices
- Additional Information
- Multicast Protocols Feature Guide for Routing Devices
Understanding Multicast Snooping and VPLS Root Protection
Snooping occurs when a Layer 2 protocol such as a spanning-tree protocol is aware of the operational details of a Layer 3 protocol such as the Internet Group Management Protocol (IGMP) or other multicast protocol. Snooping is necessary when Layer 2 devices such as VLAN switches must be aware of Layer 3 information such as the media access control (MAC) addresses of members of a multicast group.
VPLS root protection is a spanning-tree protocol process in which only one interface in a multihomed environment is actively forwarding spanning-tree protocol frames. This protects the root of the spanning tree against bridging loops, but also prevents both devices in the multihomed topology from snooped information, such as IGMP membership reports.
For example, consider a collection of multicast-capable hosts connected to two customer edge (CE) routers (CE1 and CE2) which are connected to each other (a CE1–CE2 link is configured) and multihomed to two provider edge (PE) routers (PE1 and PE2, respectively). The active PE only receives forwarded spanning-tree protocol information on the active PE-CE link, due to root protection operation. As long as the CE1–CE2 link is operational, this is not a problem. However, if the link between CE1 and CE2 fails, and the other PE becomes the active spanning-tree protocol link, no multicast snooping information is available on the new active PE. The new active PE will not forward multicast traffic to the CE and the hosts serviced by this CE router.
The service outage is corrected once the hosts send new group membership IGMP reports to the CE routers. However, the service outage can be avoided if multicast snooping information is available to both PEs in spite of normal spanning-tree protocol root protection operation.
 | Note: You can configure multicast snooping to ignore messages about spanning tree topology changes for the virtual-switch routing-instance type only. |
Related Documentation
- MX Series
- VPLS Multihomed Layer 2 Ring and MPLS Infrastructure Overview in the Junos OS Layer 2 Switching and Bridging Library for Routing Devices
- Multicast Snooping on MX Series Routers in the Junos OS Layer 2 Switching and Bridging Library for Routing Devices
- Configuring Multicast Snooping to Ignore Spanning Tree Topology Change Messages in the Junos OS Layer 2 Switching and Bridging Library for Routing Devices
- Example: Configuring Multicast Snooping for a Bridge Domain in the Junos OS Layer 2 Switching and Bridging Library for Routing Devices
- Additional Information
- Multicast Protocols Feature Guide for Routing Devices
Published: 2013-07-31
Supported Platforms
Related Documentation
- MX Series
- VPLS Multihomed Layer 2 Ring and MPLS Infrastructure Overview in the Junos OS Layer 2 Switching and Bridging Library for Routing Devices
- Multicast Snooping on MX Series Routers in the Junos OS Layer 2 Switching and Bridging Library for Routing Devices
- Configuring Multicast Snooping to Ignore Spanning Tree Topology Change Messages in the Junos OS Layer 2 Switching and Bridging Library for Routing Devices
- Example: Configuring Multicast Snooping for a Bridge Domain in the Junos OS Layer 2 Switching and Bridging Library for Routing Devices
- Additional Information
- Multicast Protocols Feature Guide for Routing Devices
